PROJECT SUMMARY Long-term heavy alcohol drinking causes organ injury, and multiple lines of evidence support a critical role of the intestine in alcohol-induced pathogenesis. Alcohol disassembles intestinal tight junctions and increases gut permeability to macromolecules. Alcohol also causes dysbiosis, an increase in pathogenic bacteria and a decrease in commensal bacteria. Consequently, alcohol increases translocation of the pathogenic bacteria and/or bacteria products and induces inflammation in multiple organs, particularly in the liver. Therefore, intestine is a major site to generate systemic factors mediating alcohol-induced organ injury. Recent studies demonstrated that reduced expression of intestinal antimicrobial peptides (AMPs) accounts for the alcohol- induced pathogenic bacteria translocation and the development of hepatitis. However, the mechanisms of how alcohol abuse induces host-microbiota dyshomeostasis remain largely unknown. The intestinal innate immune system plays a crucial role in maintaining the symbiotic balance between the host and gut microbiota by restricting the growth of pathogenic bacteria. In the past granting period, we have shown that alcohol exposure causes accumulation of acetaldehyde (AcH) not only in the liver and plasma but also in the intestinal tissues and lumen contents. The intestinal AcH levels correlated with alcohol-induced gut permeability increase and enteric dysbiosis as well as endotoxemia and hepatic inflammation. Most importantly, we demonstrated that a- defensins and lysozyme produced from the intestinal Paneth cells were reduced by alcohol exposure in association with the development of enteric and hepatic dysbiosis and hepatitis. Our findings suggest that AcH- induced Paneth cell dysfunction may represent an important mechanism underlying alcohol-induced disorders at the gut-liver axis. Paneth cells at the bottom of the intestinal crypts are professional AMP-producing innate immune cells, and the role of Paneth cell dysfunction in alcohol-induced pathogenesis at the gut-liver axis has not been defined. This project aims to determine if Paneth cell dysfunction is a crucial factor in alcohol-induced intestinal overgrowth of pathogenic bacteria, gut permeability increase, bacteria/bacteria products translocation and hepatic inflammation.